Oil weight for 2000 Civic EX

I have a 2000 Honda Civic EX with almost 170K miles. I change my own oil using Castrol high mileage. Been using 10W-30, but the oil cap says 5W-30. At a loss here. Any suggestions or advice?

The best suggestion is the one the manufacturer printed on the oil cap. The manufacturer’s tech writers, working from the design package, elaborated in the owner’s manual.

It would be foolhearty of me to suggest that I know more than the guys that designed and tested the thing. They did accelerated life testing, environmental testing, and countless other endurance and wear tests and analysis. Hey what’s the plural of analysis anyway? Analysises?

Why are you at a loss? The cap says use 5W-30 and you can buy 5W-30 in Castrol High Mileage at Walmart. So, what’s the problem use 5W-30. If you live in Florida, Arizona or some other warm weather year round state and want to use 10W-30 no big deal. If you live in cold climates the 5W-30 will make it easier on your starting motor, will circulate and lubricate better as the car warms up, and you’ll get more mpg.

Whatever you do, it won’t make a lot of difference. So, why not use 5W-30 as the cap states.